Petroleum feeds such as residuum feeds, particularly bitumen (heavy oil), are laden with high levels of heteroatoms (nitrogen, oxygen and sulfur) and metals (nickel, vanadium and iron). Petroleum feeds such as naphtha and distillate fractions also can contain undesirable levels of such heteroatoms. With environmental constraints continually lowering the allowable amounts of sulfur in such oils, economical processes are necessary to refine or upgrade the oils into acceptable products.
Heavy oils have been desulfurized in prior art processes using metallic sodium via the following route. Disadvantageously many steps are then needed to separate the product oil and to regenerate the metallic sodium. EQU R'--S--R+2Na+H.sub.2.fwdarw.R--H+R'--H+Na.sub.2 S (1)
Thus in these processes the desulfurization reaction requires one mole of hydrogen and two moles of sodium per mole of sulfur removed, one mole to form a sodium mercaptide salt intermediate (R--S.sup.- Na+, where R represents an organic moiety in the oil) and the second mole of sodium to remove the sulfur from the oil by and forming sodium sulfur (Na.sub.2 S). The Na.sub.2 S byproduct has a melting point of about 1,180.degree. C. To facilitate recovery of the Na.sub.2 S using liquid--liquid separation, the salt is converted to the more easily separated sodium hydrosulfide (NaSH, melting point of 350.degree. C.) by treating with hydrogen sulfide (H.sub.2 S) in a subsequent quench step. For regeneration of the metallic sodium, the NaSH is first treated with elemental sulfur to generate sodium tetrasulfide (Na.sub.2 S.sub.4) and H.sub.2 byproduct. The Na.sub.2 S.sub.4 is then processed through an electrolytic cell to generate Na and sodium pentasulfide (Na.sub.2 S.sub.5). The pentasulfide can then be pyrolyzed to yield the tetrasulfide (which can be recycled to the electrolytic cell) and elemental sulfur. The many separate steps of the prior art processes are lengthy, time consuming and costly.
How efficiently the sodium functions in the above described system to remove organically bound sulfur from oils is measured by "Na Efficiency". This value represents the efficiency of the charged sodium in desulfurizing the oil relative to forming Na.sub.2 S, wherein the second mole of Na cleaves the R--S.sup.- Na+ salt intermediate to form the Na.sub.2 S product. The equation for determining % Na Efficiency is as follows: ##EQU1##
Sodium metal desulfurization is disclosed in U.S. Pat. Nos. 3,785,965; 3,787,315; 3,788,978; 3,791,966; 3,796,559; 4,076,613 and 4,003,824. This earlier art describes the addition of hydrogen solely for capping the R.cndot. radicals formed and the prevention of retrograde condensation reactions. The latter of which reduce yield and oil quality. In the prior art, 438.degree. C. temperatures are described for as much as 60 minutes treatment time and hydrogen was used. In these prior art, sodium efficiencies of 60-80% are typically achieved.
Sulfur laden petroleum feeds, such as heavy oils, including bitumen, have been desulfurized by treatment with sodium metal and small amounts of hydrogen. This process is not commercialized today because regeneration of the sodium metal is costly. What is needed is an economical method for desulfurizing petroleum feeds. The process of this invention provides this benefit.